1. Field of the Invention
This invention relates to a method for making a slotted bolt, more particularly to an apparatus for forming a slot in an end surface of a semi-product of a bolt prior to thread formation.
2. Description of the Related Art
Referring to FIG. 1, in a case where threads of a set bolt 1 are formed prior to formation of a slot 10 (shown in slotted lines) in an upper end surface of the bolt 1 by a lathe in a known manner, several tabs 11 (only one is shown) may be created on the bolt 1 at positions adjacent to two end portions of the slot 10. In this case, it is necessary for the bolt 1 to undergo vibration processing in order to have the tabs 11 drop therefrom. To enable removal of the tabs 11 from the bolt 1 by vibration, the bolt 1 is made of high speed steel, thereby resulting in increased manufacturing costs. Because the slot 10 is formed by means of a lathe, the production efficiency is reduced, and a large amount of metal waste is created.
Referring to FIG. 2, in a case where a slot 10' is formed in an upper end surface of a bolt 1' prior to formation of threads by a lathe in a known manner, several sharp projections 12 may be formed on the bolt 1' in two end portions of the slot 10', thereby obstructing insertion of a wedge-shaped end of a screwdriver into the slot 10'. As a result, this slot forming process is seldom adopted by manufacturers of slotted-bolts.